Because a lot of the current attention around iPhones has to do with the latest and greatest iPhone 5, it’s easy to forget that there are plenty of older devices to be dealt with around the world. While recycling may be an option for much older devices, the iPhone 4 and 4S, at least, are helping to create a second-hand market that is both robust and global.

The market, says The Wall Street Journal, tends to be mostly US to overseas in direction and is growing in response to the high visibility of the iPhone brand via the iPhone 5. An entire industry has grown up around the resale of older iPhone devices.

“We are supply constrained. There is insatiable demand for this product,” said Israel Ganot, chief executive of buyback service Gazelle Inc.